Takes2-2tango,
“One what is the minhag based on ,assuming there is even a minhag.”
I don’t think anyone here is claiming that there is a minhag to be vague about or to not share the due date. Rather it is done for the reason Syag stated above – to avoid a fixation on the due date that can cause stress for the expecting parents at a time when they really, really don’t need any extra stress. Only 5% of women actually give birth on their due date – it’s a very flat curve with a standard distribution of over 2 weeks (!!) Around a quarter of women don’t give birth even within 10 days of the due date.
“2)Even if yoi wont give an exact date, why cant you give an approximation. +/- 2 weeks.”
I don’t understand why you are asking iacisrmma this – s/he has already stated that this is what they do.
“I know people who over all very logical/mentchlich people ,but when it comes to telling parents/ inlaws they act as if its non of your business to ask or know. “
Perhaps the reason some couples are more hesitant to tell parents is that the parents are much more invested than friends, and thus unfortunately more likely to generate the late pregnancy stress – especially if they are not sensitive or understanding. That said, I agree with Joseph’s point regarding kibud av v’eim. So my personal opinion would be to give the general idea as iacisrmma does, and tell the parents that we are not relying on the due date provided by the doctors, because it doesn’t have much meaning and that focusing on a specific date causes distress. So no real information is being withheld at all. I think most loving parents would be fine with that.